Kathryn Mewes tells Rachel Carlyle how she can settle your troublesome child in just three days

It's always a touch embarrassing for parents to admit they have somehow ended up with a five-year-old who will eat only fish fingers or a nine-year-old who won't sleep in their own bed -- and most would happily throw their arms round the person who promised to straighten out their offspring in just three days.

Kathryn Mewes has had that reaction many times from the hundreds of parents she has worked for as the "Bespoke Nanny", moving into the home for three solid days to sort out food and sleep problems (the most common) or out-of-control behaviour. She has dealt with all ages from babies to teenagers and is confident that three days is enough.

"Put it this way, out of the last 80 families I have worked with I have had to spend an extra day with only two -- and that was because the parents didn't have the confidence to follow it through, not because of the children," she says.

Mewes (38) was a Norland nanny with 16 years' experience before she started the three-day nanny business from her home in Clapham, South London. Her warm but unswerving smile has a touch of the Mary Poppins about it and she is a familiar sight on the better streets of London with her tweed jacket and bottle-green Pashley bicycle, complete with basket for her handbag (which is, disappointingly, Mulberry rather than tapestry).

Mewes has distilled her methods into a book, The 3-Day Nanny, and promises parents can achieve the same results as long as they are prepared to cancel everything else for three days and follow it through consistently.

She believes that almost all the problems she has encountered -- such as the six-year-old girl getting up 30 times a night or the eight-year-old boy viciously attacking his mother -- are caused by parents unintentionally losing control.

"I think it's because we have left it later in life to have children and we know how hard it can be to have a child, so of course we want everything and more for that child," she explains. "Saying 'yes' is easier than saying 'no' so, in the case of food, if they want fish fingers every day we say 'yes'. Then you've got a child who will eat only fish fingers."

She hit on the three-day idea when she discovered that she was rarely staying at clients' houses longer than that. It also has a sound academic basis: psychiatrists call it social learning theory, where behaviours are changed incrementally and small steps rewarded.

Mewes explains to the child how things are going to change and why. They are given clear boundaries, encouragement and rewarded with stickers (for younger children) and magnetic stones (for older ones, which they build into a tower. When it reaches the agreed height a treat is due).

Many parents are initially sceptical, despite parting with her daily fee of £500 (€625). "I have had plenty -- especially dads -- say: 'I can't believe we have spent so much money for a woman with a load of stones.' But they're my favourite cases because they are so amazed when it works."

The three days generally follow a pattern: refusal and fighting on day one, grudging acceptance on day two and enthusiasm for the new regime on day three.

"I always say to parents: 'If you can get through day one you are near enough there,'" says Mewes, who adds that she has never raised her voice to a child in 20 years, and the parents who can afford it usually want her to stay on after the three days are over.

She tells parents to find their own "firm voice".

"Most parents I know go from zero to volume 10 -- shouting. They miss out the middle bit, which is the firm voice. You bend down, look at them -- if you're not looking at a child, you can guarantee they are not listening to you -- and drop a tone so your voice is lower and firmer." They also need a sanction; Mewes has the "thinking space", her version of the naughty step, where children go, alone, when they haven't done what is asked.

Cleverly, children are given the illusion of choice, so they still feel they have some control. In the case of a boy who wouldn't put on his coat for school, she advised the parent to buy a pink coat from a charity shop to hang next to his blue one. "Then we'd say: 'Are you going to wear the pink or blue coat today? Shall I choose today? I think I fancy pink.' Then I'd go away and make a cup of tea and let him think. You are guiding them towards the right choice."

Most of us would give up at this point because we would be late for school, but it's vital to plough on.

"If you are half-an-hour late because you need to show control then so be it. The next day you can be sure they will put their coat on."

Despite being warm and witty in the flesh, Mewes does worry about sounding overly nannyish in the book, and she is clearly nervous about suffering the same fate as the "Queen of Routine" Gina Ford and "Supernanny" Jo Frost, who came under attack from some parents because they had no children themselves.

"All I will say is that my dream is to have children, but at 38 it does not come quite so easily," she says. "I know I have no right to be judgmental.

"I meet so many high- flying women and think: 'If it can happen to them it can happen to anyone.' But it shouldn't matter that someone has made a mistake. Children don't come with instruction manuals and in three days we can fix anything."